Conventionally, charge-pump step-up circuits have been often used as power supply circuits for obtaining, from a power supply voltage, an output voltage that is higher than the power supply voltage. Typically, such a charge-pump step-up circuit is configured as follows. A plurality of stages of charge pump units, each being composed of a flying capacitor and a switch, are sequentially connected so as to obtain an output voltage by stepping up an input voltage to a predetermined level (see Patent Document 1).
In the charge-pump step-up circuit described above, to obtain an output voltage at a predetermined level, stepping-up operation performed thereby has to be controlled according to its output voltage. As an example of a conventional technology related to what has been described thus far, Patent Document 2 discloses a stepping-up operation control method by which an output voltage of the step-up circuit is detected, and, according to the output voltage thus detected, the conductivity of a MOS transistor provided in the step-up circuit is controlled.
Patent Document 1: JP-A-2003-234408
Patent Document 2: JP-A-H06-351229